This invention relates to a system, method of measurement, and presentation of motion within a cavity, used for example to determine the magnitude of blood perfusion to a tissue located within a body cavity.
When living tissue is illuminated by laser light the light reflected off the natural surface irregularities interferes constructively and destructively producing a random interference pattern called speckle. The speckle pattern produced by a stationary object remains static in time and is said to have a high speckle contrast. If the object contains several individual particles undergoing motion, such as red blood cells, then the phase difference between the interfering beams will change in time. The resulting changes in light intensity reflecting off the tissue can be measured and analyzed to produce an index linearly related to tissue blood flow. Using this principle, Stern et. al. developed a technique for measuring skin blood flow using a collimated laser beam, pinhole aperture and photomultiplier tube (M. D. Stem, “In vivo evaluation of microcirculation by coherent light scattering”. Nature, 254, pp 56-58, 1975.)
Imaging techniques for mapping tissue blood flow have subsequently evolved from Stem's work and are known in the art as laser speckle methods. Fercher and Briers applied laser speckle using a photographic method for capturing speckle contrast images, an optical filtering technique for mapping retinal vascular structure and a region of tissue fully illuminated by laser light (A. F Fercher and J. D. Briers, “Flow visualization by means of single-exposure photography”. Optics Communications. 37:5, 326-330, 1981.)
More recently Briers described a speckle imaging method that used a CCD camera and electronic processing rather than photography and optical filtering techniques. He used this method to generate blood flow maps of skin rather than retinal blood flow (J. D. Briers, G. R. Richards, and X. W. He, “Capillary blood flow monitoring using laser speckle contrast analysis (LASCA)”, J. of Biomed. Opt. 4:1, pp. 164-175, 1999; J. D. Briers, and S. Webster, “Quasi real-time digital version of single-exposure speckle photography for full-field monitoring of velocity or flow fields”. Opt. Comm. 116, pp 36-42, 1995). A limiting feature of Brier's technique is that the electronic image processing method for determining speckle contrast requires a 7×7 pixel window. This window reduces the original speckle images from 512×512 pixel to 73×73 pixel resolution, resulting in a very low-resolution blood flow map. Another limiting feature is that the Brier contrast method for generating blood flow maps is not a relative measure of blood flow and can only be used to display the sharp contrast between areas of high flow embedded within a stationary or (comparably low flow) surrounding tissue matrix. Although speckle contrast images are useful for displaying tissue vascular structure, they do not provide a clinical technique for the immediate and visual display of “true” blood flow maps, where each pixel within the image is linearly related to blood flow and several images can be captured for the dynamic measurement of relative blood flow and blood flow changes. More recently Dunn and co-workers have used the Brier contrast method to produce cerebral blood flow maps (A. K. Dunn, H. Bolay, M. A. Moskowitz, and D. A. Boas, “Dynamic Imaging of Cerebral Blood Flow Using Laser Speckle”. Journal of Cerebral Blood Flow and Metabolism 21, 195-201, 2001) where the CCD camera is placed directly above a few millimeters area of surgically exposed cerebral tissue.
Another laser speckle technique is presented in U.S. Pat. No. 4,862,894 and has been specifically applied to the measurement of skin blood flow (H. Fujii, et. al. “Evaluation of blood flow by laser speckle image sensing”, Applied Optics 26:24, pp. 5321-5325, 1987) and subchondral bone blood flow (S. Fukuoka, T. Hotokebuchi, K. Terada, N. Kobara, H. Fujii, Y. Sugioka, and Y. Iwamoto, “Assessment of subchondral blood flow in the rabbit femoral condyle using the laser speckle method.” J. of Orth. Res., 17, pp 368-375, 1999; S. Fukuoka, T. Hotokebuchi, S. Jingushi, H. Fujii, Y. Sugioka, and Y. Iwamoto, “Evaluation of blood flow within the subchindral bone of the femoral head: Use of the laser speckle method at surgery for osteonecrosis.” J. of Orth. Res., 17, pp 80-87, 1999). This instrument uses a one-dimensional photo-detector array and a scanning arrangement to produce two-dimensional maps of tissue blood flow rather than a CCD camera. A collimated laser line is projected onto the tissue surface and the resultant line of speckles is simultaneously focused onto the linear CCD device. A time differentiated technique for measuring blood flow is applied rather than the method of measuring speckle contrast so a very fast CCD readout device with consequent low resolution is required. Using the scanning mirror assembly, Fujii and co-workers produce a two-dimensional map of tissue blood flow with a typical pixel resolution of 128×64 (Fuji, 1987). More recently Fujii has replaced the scanning mirror sensor with a high-speed, two-dimensional, image sensor (100×100 pixels) and modified the above time differentiated speckle technique into an ophthalmic device for measuring retinal microcirculation (N. Konishi and H. Fujii, “Real time visualization of retinal microcirculation by laser flowgraphy”. Opt. Eng. 34, No. 4, pp 753-757, 1995; Y. Tamaki, M. Araie, E. Kawamoto, S. Eguchi, and H. Fujii, “Noncontact, Two-dimensional measurement of retinal microcirculation using laser speckle phenomenon”. Inv. Opth. And Vis. Sci., 35, No. 11, pp 3825-3834, 1994). This laser speckle technique is described in U.S. Pat. Nos. 5,163,437 and 5,240,006. It is specifically designed for ophthalmic work and small field of views related to the size of the eye fundus.
No speckle imaging technique described in the cited art is adapted or could be used for endoscopy. A common feature of all of speckle imaging techniques described in the cited art is that they are remote techniques, which require the instrument to be placed directly above or in front of the tissue surface. Remote speckle imaging techniques require fixation of the instrument and the tissue surface. During endoscopic speckle imaging, the surgeon and patient may be expected to move and cause distortion and artifact in the image. Another common feature of prior art speckle imaging techniques is that their image resolution is too low to be useful for clinical endoscopy. Endoscopy is a technique that requires immediate visual display to assist in cavity navigation and tissue recognition, and serious surgical decisions are often made based on what the surgeon “sees”. The minimum image resolution required for clinical endoscopy is a standard video resolution of 640×480 pixels. This resolution is maintained for a variable field of view that can range from a few square millimeters to several square centimeters. Prior art speckle-imaging techniques are limited in a low resolution and restricted field of view. Therefore, applying prior art speckle techniques to endoscopy would result in an image that is of too low of resolution or much too small to be clinically useful.
Presently, endoscopic surgery is conducted routinely in hospital operating rooms on a daily basis. Much orthopedic endoscopic surgery is devoted to diagnosis of underlying conditions such as injury, inflammatory arthritis and osteoarthritis. In the surgical art diagnostic information is based on tactile and visual inspection of the tissue through the endoscope. While this information renders data pertaining to the structure of the tissue under examination, it does not provide information about the functional integrity of the tissue structures. Those skilled in the surgical arts would expect the assessment of the metabolic state of tissue physiology in response to injury or inflammation to provide a useful diagnostic. For example such a diagnostic would be useful in determining whether tissue should be repaired or resected when the predicted outcome of healing, based on such endoscopic tactile and visual inspection of tissue anatomy, is uncertain.
Those skilled in the surgical art would expect that measuring tissue temperature could be used to assess the metabolic state of tissue. For example it is well known that the inflammatory response of tissue to injury results in local elevation of tissue temperature. The measurement of tissue temperature in a manner that does not perturb the measurement is problematic. The use of thermometry to assess the metabolic state of tissue has limited clinical relevance because the measurement is local to the point of tissue contact. More recently the methods of thermography have been used to assess tissue metabolic state, in particular for the diagnosis on malignancy. This method relies upon the imaging of mid infrared radiation emitted for tissue. Mid infrared radiation will not transmit through the materials of the imaging optics used in endoscopes so the use of thermography in combination with an endoscope is not possible.